The present invention relates to an ultraviolet-curable silicone composition. More particularly, the invention relates to an organopolysiloxane-based composition curable by irradiation with ultraviolet light and capable of giving a cured film having surface releasability against adhesive or sticky surfaces to find usefulness as a back-surface treatment agent for pressure-sensitive adhesive tapes and coating agent on a releasable protective sheet for pressure-sensitive adhesive labels and adhesive fixing fastener tapes for, e.g., disposable diapers.
As is well known, ultraviolet-curable silicone compositions are old and many proposals were made heretofore for various types of such compositions. Among them, in particular, it is only in recent years that a large number of proposals are made for an ultraviolet-curable silicone composition comprising an organopolysiloxane having epoxy groups in the molecular structure and an onium salt compound which acts, when the composition is irradiated with ultraviolet light, as a photoreaction-initiator to effect curing of the composition (see, for example, Japanese Patent Publication 02-38602 and Japanese Patent Kokai 3-128975). As compared with an ultraviolet-curable silicone composition by utilizing the mechanism of a radical reaction for ultraviolet-induced curing of the silicone composition, the curing reaction in the ultraviolet-curable silicone composition of the above-mentioned type is little susceptible to the inhibition by oxygen in the air so that the silicone compositions can be cured satisfactorily by irradiation with ultraviolet light even in the atmospheric air. Accordingly, the ultraviolet-curable silicone compositions based on an epoxysilicone and an onium salt compound are expected to be widely employed in the above-mentioned applications.
As a trend in recent years, taping and labeling works with pressure-sensitive adhesive tapes or labels are conducted mostly by utilizing a machine which works sometimes at a great velocity necessarily resulting in an increased peeling resistance on the releasable sheet eventually accompanied by a trouble of vibrations of the tapes or labels usually with generation of so-called peeling noises by which deterioration of the working environment due to noisiness is unavoidable.
Since generation of a peeling noise is a result of fluctuating variations in the peeling resistance of the releasable sheet, a large fluctuation in the peeling resistance not only causes a large peeling noise but also greatly disturbs normal running conditions of the taping or labeling machine which is designed and constructed under a presupposition of a constant peeling resistance.
Plastic film-based pressure-sensitive adhesive tapes are sometimes used as a fastener tape for fixing a disposable paper diaper around the waist of the wearer. While it is necessary that, in order to ensure stability of the diaper around the waist, the peeling resistance of the fastener tapes is considerably high, a large peeling force of the fastener tape necessarily leads to generation of an unpleasant peeling noise when the fastener tape is peeled off in removal or re-fitting of the diaper. Since diapers are used as a daily commodity, generation of a large peeling noise from the fastener tapes is naturally undesirable and should be avoided without undue decrease in the peeling resistance of the fastener tapes to ensure fitting stability of the diapers.